Los Angeles County public works officials have asked the MTA to explain why a section of the Los Angeles River has sunk more than 2 inches since subway work crews began tunneling under it in 1996.
"We want to know what's going on," said Lance Grindle, the supervising engineer who oversees permits for the flood-control channel. "I think there's been a gradual settlement. It has exceeded the initial settlement we thought we'd get."
Reports from the transit agency indicate a segment of the concrete-lined riverbed in North Hollywood has sunk about 2 1/2 inches, Grindle said. A surveyor for the Metropolitan Transportation Authority examined the channel Wednesday, and found it had not slipped any further in the past six months, MTA spokesman Ed Scannell said.
While public works officials expected a maximum 1 1/2-inch sinkage when they authorized the transit agency to dig under the river, Grindle said the extra inch did not appear to pose a threat.
Ultimately, if the channel were to develop severe cracks, the rushing waters that flow through it after rainstorms could seep into the ground around the channel and saturate it, but Grindle minimized the likelihood of such an event.
Critics of the MTA, such as state Sen. Tom Hayden (D-Los Angeles), said the public works department could have averted the sinkage if it had reviewed the MTA's plans more carefully before granting it a permit.
Public works officials approved the permit in May 1996, about six weeks faster than usual, without requiring the MTA to fully explain the tunneling risks. MTA officials were under pressure to have the permit approved quickly, because if tunneling work had halted, the contractor would have been able to bill the transit agency an extra $50,000 per day.
"Can it get any worse?" Hayden asked. "You need checks and balances instead of collusion between these agencies."
Grindle defended the department, saying it had been monitoring the channel with its own surveyors.
MTA officials have fielded thousands of claims and lawsuits arising from ground slippage associated with the tunnel. The transit agency and its insurance company have paid at least $15 million in related settlements and judgments.
In addition to the 70-foot-wide sinkhole that opened on Hollywood Boulevard in 1995, the MTA acknowledged in 1996 that a segment of the Hollywood Freeway in Studio City sank over excavation work.